RE: Asunto: Re: An even dumber question

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> SOTO@ADINET.COM.UY
>
> Mike Keesey wrote:
>
> >More recently, _Dinosauria_ has been defined as a phylogenetic taxon, a
> clade.
> >One proposed definition would be: "The last common ancestor of _Iguanodon
> >bernissartensis_ and _Megalosaurus bucklandii_, plus all of that
> ancestor's
> >descendants."
>
> And what about the diagnosis of Dinosauria? For example, are Novas' (1996)
> synapomorphies still valid or some of them has shown to diagnose more or
> less inclusive clades?
> Thanks,

Yes.  Some are still valid, some diagnose more inclusive clades, some
diagnose less inclusive clades.  This depends on a number of things: in
particular, the phylogenetic position of Silesaurus and what the heck the
rest of the anatomy of Lewisuchus and/or Pseudolagosuchus, Lagosuchus,
Marasuchus (if it really is different from the former), Lagerpeton, etc.,
look like. Heck, for that matter, we need to know what Pisanosaurus really
looks like!

Something that people have to accept is that diagnoses are, and always will
be, subject to revision with new information.  We are mere mortals and will
always lack total knowledge of every aspect of every taxon at every life
stage, including all individual variation.

With regards to the practical end of your question: Adam Yates, Max Langer,
and others are undergoing pretty substantial revisions of basal saurischians
of various sorts. With that information at hand, we can better characterize
the states present in the common ancestor of all saurischians, at least.
This work is currently in progress, so one has to wait a little bit (some
before year's end, though!) before it is available.

Hope this helps,

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796